Tripping system for circuit breaker

ABSTRACT

A current limiting circuit breaker is constructed to achieve more rapid tripping in the medium fault current range by utilizing a magnetic tripping device which imparts physical motion to the movable contact under particular fault current conditions. In the lowest fault current range above the thermal tripping range the magnetic tripping unit automatically operates or releases the spring operating mechanism thereby causing contact separation. As fault current increases the magnetic tripping means is effective to assist the operating mechanism to physically move the movable contact, and at still higher currents the magnetic tripping means moves the movable contact to its fully open position before any movement is imparted to the movable contact by the spring operating mechanism. As fault currents increase still further, electrodynamic forces assist the magnetic means to physically move the movable contacts, and in the very highest fault current range electrodynamic operation moves the movable contact essentially to its fully opened position, before the magnetic trip means for the operating mechanism is active in moving the movable contact.

[54] TRIPPING SYSTEMFOR cmcmr- BREAKER [72] Inventors: Frank W. Kussy,Haverford; Gustave E. Heberlein, Jr., King-0f Prussia, both of Pa.

[73] Assignee: I-T-E Imperial Corporation, Philadelphia, Pa.

[22] Filed: Dec. 20, 1971 [21] Appl. No.: 209,853

Related US. Application Data [62] Division or Ser. No. 145,175, May 20,1971,

Pat. No. 3,663,903.

521 uscn ..3s5/255,335/17e 51 rm. c1. .Htllh 3/52 58 newer Search..335/258, 261, 279,255,281, ass/19,174

[56] I References Cited UNITED STATES PATENTS 2,829,319 4/1958 McCleskey..-...335/25s 2,570,062 10/1951 Kesselring ..335/19 [15] 3,7 ill f ,35[451 Nov. 28, E972 57 TRACT A current limiting circuit breaker isconstructed to achieve more rapid tripping in the medium fault currentrange by utilizing a magnetic tripping device which imparts physicalmotion to the movable contact under particular fault current conditions.In the lowest fault current range above the thermal tripping range themagnetic tripping unit automatically operates or releases the springoperating mechanism thereby causing contact separation. As fault currentincreases the magnetic tripping means is effective to assist theoperating mechanism to physically move the movable contact, and at stillhigher currents the magnetic tripping means moves the movable contact toits fully open position before any movement is imparted to the movablecontact by the spring operating mechanism. As fault currents increasestill further, electrodynamic forces assist the magnetic means tophysically move the movable contacts, and in the very highest faultcurrent range electrodynamic operation moves the movable contactessentially to its fully opened position, before the magnetic trip meansfor the operating mechanism is active in moving the movable contact.

3 C, 16 Drawing Figures TRIPFING SYSTEM FOR CIRCUIT BREAKER This is adivisional application of Ser. No. 145,175, filed May 20, 1971, now US.Pat No. 3,663,903.

This invention relates to circuit breakers in general, and moreparticularly relates to a current limiting circuitbreaker having meansto increase the speed of contact separation in the medium fault currentrange.

In current limiting circuit breakers of the. prior art utilizingelectrodynamic effects for current limiting action, in the range ofmedium fault currents there apcontact operating mechanism is effectiveto move the contacts. In the lowerportion of this range the magnetictripping means and the contact operating means complement one another inbringing about contact separation. However, in the upper portion of thisrange,

contact separation is essentially completed before the contactoperatingmechanism acts to separate the contacts. Above this latterrange electrodynamic effects assist the magnetic tripping means toseparate the contacts, and at still higher currents electrodynamiceffects operate the movable contact essentially to its fully openedposition before either the tripping mechanism or the contact operatingmechanism is effective to move the movable contact.

Accordingly, a primary object of the instant invention is to provide anovel construction for a current limiting circuit breaker.

Another object is to provide a circuit breaker of this type in which thespeed of contact separation in the medium fault current range isincreased.

Still another object is to provide a circuit breaker of this type inwhich there is a novel magnetic tripping means that is effective tophysically move movable contacts upon the occurrence of predeterminedfault currents.

A further object is to provide a circuit breaker of this type in whichthere is coordination between an overcenter spring operated mechanism,an electromagnetic tripping device, and electrodynamic means to achievea relatively smooth tripping characteristic.

A still further object is to provide a circuit breaker having a trippingelectromagnet with a novel armature construction.

These objects as well as other objects of this invention will becomereadily apparent after reading the following description of theaccompanying drawings in which:

FIG. I is a graph showing a comparison between the trippingcharacteristics of a current limiting circuit breaker constructed inaccordance with the instant invention'and a current limiting circuitbreaker of the prior art.

FIG. 2 is a side elevation of a molded case current limiting circuitbreaker constructed in accordance with teachings of the instantinvention, with the near side of the housing removed to reveal theessential operating and current carrying elements.

FIG. 3 is a fragmentary portion of FIG. 2, illustrating contact openingdue solely to action of the spring operating mechanism.

FIG. 4 is a fragmentary portion of FIG. 3, illustrating contact openingunder conditionswhere the magnetic tripping device exerts a mechanicalforce to assist the spring operating mechanism.

FIG. 5 shows the elements of FIG. 4 when contact opening is due solelyto mechanical'forces developed by the magnetic tripping means.

FIG. 6 is a fragmentary portion of FIG. 3, illustrating contact openingunder conditions where electrodynamic forces assist the mechanical forceof the magnetic tripping means.

FIG. 7 shows the elements of FIG. 6 under conditions where contactseparation is due solely to electrodynamic forces.

FIGS. 8 and 9 are perspectives of the movable stationary contactslooking at opposite sides thereof.

FIG. III is an end view of the contacts looking in the direction ofarrows ltl lll of FIG. 8-

FIG. I1 is an end view ,of the contacts looking in the direction ofarrows 11-11 of FIG. 9.

FIG. 12 is a view similar to that of FIG. '10 with the addition ofinsulating barrier elements.

FIG. 13 is a cross-section taken through line III-I3 of FIG. 12 lookingin the direction of arrows 13-13.

FIG. 14 is an enlarged view of the operating magnet under normal loadcurrent conditions.

FIG. 15 is a side elevation of the magnet yoke and armature under faultcurrent conditions. contacts FIG. 16 is a side elevation of the magnetarmature looking in the direction of arrows 16l6 of FIG. I5.

Now referring to the figures. As illustrated by curve A in FIG. I, thetripping characteristic of prior art molded case current limitingcircuit breakers is generally divided into two regions C and D. In thefirst region C the magnetic trip device of the breaker releases a latch,permitting energy stored in the operating springs to open the contacts.In region C, fault currents are in the low to medium range, ortypicallyfrom 5 to 5th times the maximum continuous current rating ofthe breaker, and very little current limitation takes place becausecontact opening speed is relatively slow.

In the second region D, the fault currents are higher than in region C,and the circuit breaker contacts are opened independently of the circuitbreaker operating mechanism. The major share of current limitation takesplace in region D since the contacts are opened before current hasreached the maximum available peak. At this time the onntacts are openedat a speed that is high enough to draw and develop a high are voltagewhich opposes the driving voltage of a system until current arrives atzero.

As will hereinafter be seen, circuit breaker or circuit interrupter 20(FIG. 2), constructed in accordance with the instant invention, has atripping characteristic illustrated by curve B. The differences betweencurves A and B are due to the fact that circuit breaker 2t) achievesfaster contact separation in the range of medium fault currents withoutadversely effecting tripping at low fault currents or very high faultcurrents.

Circuit breaker 20 of FIG. 2 is a multi-phase unit, only one phase ofwhich is illustrated in the drawings. In particular, circuit breaker 2%includes molded insulating compartmented hollow base 21 having removablemolded insulating cover 22 with opening 23 through which manualoperating handle 24 extends. Handle 24 controls operation'of a standardtype overcenter spring operating mechanism 25 which operatesautomatically upon the occurrence of predetermined fault conditions.Mechanism 25 includes main operating tension spring 26 connected betweenhandle 24 and knee 27 of the toggle-formed by links 28, 29.-Upper link28 is pivotally connected at 31 to cradle 32. The latter is mounted atone end topivot 33 and at its other end is provided with latch tip 34engageable by latch 36 of a standard type automatic trip mechanism 35.The latter includes thermal or bimetal tripping means (not shown) whichprovides delayed tripping under low fault conditions in the region overwhich curve portion E extends. v The lower end of lower toggle 29 isconnected by pi 37 to the main contact ,arm portion 38 which ispivotally mounted on a center extending through insulating tie bar 41..Pivot pin 40 connects auxiliary movable contact arm 39 to the end ofmain armi38 remote from tie bar 41. Bridging contact 42 (FIG. .8) ismounted to auxiliary arm 39 at the left end thereof and provides a partof the main current path through circuit trodynamic forces fro bringingabout separation of bridging contact 42 from stationary contacts 45, 46under severe fault conditions. In particular, bridging contact 42 is amodified U-shaped member including spaced parallel generally L-shapedarms 53, 54 joined by web or connecting section 52. The free ends ofarms 53 54 carry movable contacts 55, 56, respectively, which overlieand are engageable with stationary contacts 45, 46. Conductor 47 isconnected at one end to conductingblock 57 which supports stationarycontact 46. The portion 47a of conductor 47 that extends parallel andadjacent to bridging contact connecting section 52 is rigidly held withrespect to base 21.

Thus, currents I flow in opposite directions in conductors 52 and 47a sothat magnetic fluxes accompanying such currents interact to produce anelectrodynamic force indicated by double-headed arrows 61. Becauseconductor section 47a is rigidly held, this electrodynamic force movesbridging contact 42 upward with respect to FIG. 8, thereby separatingmovable contacts 55, 56 from stationary contacts 45, 46. As theseparation takes place, electric current arcs 62 are tacts 45 and 46 isa path having a narrow U-shaped section defined by the space betweeninsulating barrier 65 and the boundary surfaces of notch 66. It is notedthat inFIGS. 2-10, insulating barrier 65 is not shown nor is an arcchute shown. These elements are not present in order that the elementsshown in these Figures may be illustrated with a greater degree ofclarity.

Under overload conditions where current exceeds the current required forthermal tripping overcenter spring operating mechanism 25 is operatedthrough the action of trip bar 67 releasing latch 36 which in turnreleases latch tip 34 of cradle 32. Rod 67 is pivotally mounted at 68,and is biased in a clockwise direction by tension spring 69. The rightend of rod 67, with respect to FIG. 2, extends into trip unit 35 forreleasing latch 36, and the left end of rod 67 extends into the spacebetween adjustable collars 71, 72 mounted on trip rod 76. The latterextends upward from magnet armature 73 which constitutes the movablepart of the magnetic frame also including stationary yoke 74.

Spring 69 acting through rod 67 in engagement with collar 71 biases rodupward.

Springs 76, extending between outboard pins 76a of auxiliary arm 39 andpin 76b extending through the bifurcated sections of main arm 38, have aline of action shiftable to opposite sides of pin 40. When the line ofaction of pin 40 is below pin 40 (FIG. 2) auxiliary arm 39 is biasedcounterclockwise and springs 76 provide contact pressure.Counterclockwise movement is limited by inwardly extending vears 38awhich engage the right end of auxiliary arm-39. When the line of actionof springs 76 is moved above pin 40 (FIG. 12) arm 39 is biased clockwisewith this movement being limited by housing protrusion 77.

Under normal current conditions the current through coil 48 does notgenerate sufficient flux to move armature 73 against the upward forceexerted by spring 69. When current through circuit breaker 20 is in therange indicated by the first tripping step in FIG. 1, armature 73 isattracted to yoke 74 with a force sufficient to move rod 76 downward sothat collar 71 moves the left end of trip rod 67 downward, pivoting thelatter counterclockwise and releasing latch 36 so that the energy storedin main spring 26 is effective to pivot contact arm 38, 39 therebyseparating contact bridge 32 from stationary contacts 45, 46 (FIG. 3).

In the range of currents indicated by the second tripping step in FIG.1, during the delay in operation of mechanism 25 lower collar 72 engagesthe right end of auxiliary arm 39 and physically pivots the latter aboutpin 49 with respect to main arm 38. This relative motion between mainand auxiliary arms 38, 39 is increased as mechanism 25 moves main arm 38in its opening stroke, and in so doing moves pin 40 upward with respectto FIG. 4 relative to roller collar 72. Thus, in the second trippingstep, contact opening is achieved through the complementary action ofboth mechanism 25 and the physical force exerted by magnet 73, 74.

In the third tripping step of FIG. 1 the force exerted by magnet 73, 74is so great that the speed of movement of rod 79 causes collar 72 inengagement with auxiliary arm 39 to move contact bridge 32 to fullcontact separation position before spring operated mechanism 25 has hadtime to move main arm 38 a substantial distance if at all (See FIG. 5).

' In the fourth tripping step illustrated in FIG. 1, the conditionsprevailing in the third tripping step (See FIG. 5) are exaggerated tothe point where before main arm 38 is moved by mechanism 25 theengagement of collar 72 with auxiliary arm 39 begins to separate contactbridge 42 from stationary contacts 45, 46. However, before completeseparation takes place due to the mechanical action of magnet 73, 74,the electrodynam ic force described in detail in connection with FIGS.8-11 comes into play to assist in opening the contacts. Thus, in thefourth tripping step the mechanical force exerted by magnet 73, 74 iscomplemented by the electrodynamic force acting between conductor 47 andbridging contact 42 to bring about rapid separation of the circuitbreaker contacts.

In the fifth tripping step of FIG. 1, the current magnitude is so hightat even before spring mechanism 25 of magnets 73, 74 is effective tocause contact separation, bridging contact 32 is moved to its fullyopened position of FIG. 12 through the action of the electrodynamicforce acting between bridging contact connecting section 55 andconductor section 47a. This electrodynamic force pivots'auxiliary arm 39clockwise against the force of springs 76 thereby. moving pins 76aupward and shiftingthe line of action for springs 76. When this line ofaction moves above pin 40, or overcenter, springs 76 aid theelectrodynamic force to separate contacts 45, 46, 55, 56.

As seen in FIGS. 14-16, armature 73 is constructed in a manner to reducethe weight thereof, thereby permitting increased speed of operation.That is, the groups of arrowed generally circular lines 91, 92illustrate the loop paths for flux when magnet 73, 74 is energized.Since the shaded area 73a of armature 73 is not included. in either fluxpath 91 or 92 through stationary generally E-shaped yoke 74, the uppersurface of armature 73 is cut away to provide a V-shaped notch in theshaded area 73a, thereby substantially reducing the weight of the ironlaminations forming armature 73. These laminations are riveted to theflared out portion 81 at the lower end of rod 70.

Thus, it is seen that the instant invention provides a novelconstruction for a molded case current limiting circuit breaker, inwhich more rapid tripping action is obtained in the medium fault currentrange by utilizing mechanical forces of the tripping electromagnet tophysically move the movable contact. The characteristic tripping'curvefor the breaker constructed in accordance with this invention isrelatively smooth in that in various fault current ranges there iscomplementary action between the opening forces exerted by the springoperating mechanism, the tripping electromagnet, and the electrodynamicforces generated by currents flowing in opposite directions in adjacentconduc: tors.

Although there have been described preferred embodiments of this novelinvention, many variations and modifications will now be apparent tothose skilled in the art. Therefore, this invention is to be limited notby the specific disclosure herein, but only by the appending claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as fol- 1? An electromagnet including amagnetic frame and a coil means for: generating lines of magnetic fluxin said frame as current flows in said coil means; said frame includinga stationary part and a movable armature forming loop path means wheresaid lines of magnetic flux are located; biasing means urging saidarmature away from said stationary part to a position wherein there is asubstantial gap between said stationary part and one end of saidarmature and with said coil means energized said magnetic flux linesproviding an attracting force moving said armature to close said gap;said armature having a cutaway section located at its other end anddisposed where said lines of magnetic flux would not be located had saidcutaway section not been removed.

2. An electromagnet as set forth in claim 1 in which the magnetic frameincludes first, second and third parallel legs; said second legpositioned between said first and third legs; said loop path meansincluding a first and a second loop path; said first loop path includingsaid first and second legs and said second loop path including saidsecond and third legs; said armature constituting at least a portion ofsaid second leg; said gap being at one end of said armature; saidcutaway section being at the other end of said armature.

3. An electromagnet as set forth in claim 2 in which the cutaway sectionis substantially V-shaped.

1. An electromagnet including a magnetic frame and a coil means forgenerating lines of magnetic flux in said frame as current flows in saidcoil means; said frame including a stationary part and a movablearmature forming loop path means where said lines of magnetic flux arelocated; biasing means urging said armature away from said stationarypart to a position wherein there is a substantial gap between saidstationary part and one end of said armature and with said coil meansenergized said magnetic flux lines providing an attracting force movingsaid armature to close said gap; said armature having a cutaway sectionlocated at its other end and disposed where said lines of magnetic fluxwould not be located had said cutaway section not been removed.
 2. Anelectromagnet as set forth in claim 1 in which the magnetic frameincludes first, second and third parallel legs; said second legpositioned between said first and third legs; said loop path meansincluding a first and a second loop path; said first loop path includingsaid first and second legs and said second loop path including saidsecond and third legs; said armature constituting at least a portion ofsaid second leg; said gap being at one end of said armature; saidcutaway section being at the other end of said armature.
 3. Anelectromagnet as set forth in claim 2 in which the cutaway section issubstantially V-shaped.